Old feed in a silo is thought to be the most likely cause of the case of classical bovine spongiform encephalopathy (BSE) on a Somerset farm.

On September 17, 2021, the Chief Veterinary Officer and Animal and Plant Health Agency (APHA) confirmed the case of BSE - the first in the UK since 2018.

The report published today (December 17) by APHA states that the animal involved died on the small-medium mixed dairy and beef farm.

It was tested for BSE as part of controls and it was not destined to the food chain, so there has been no risk to food safety or public health.

Investigations have concluded that the most likely source of the BSE was residual material in a pre-1996 silo, a silo in use before the introduction of the reinforced feed ban.

The silo could have contained small amounts of feed produced before the reinforced feed ban, caught up in the internal structure, which became dislodged in 2015 or 2016 and entered the cattle rearer ration, and was subsequently fed to the cow.

The case was a homebred dairy cow born in February 2015 that had calved four times.

Clinical signs were first noted on 1 September 1 when milk fever (hypocalcaemia) was suspected, but she was unresponsive to treatment and so was euthanised on farm the following day.

Following a positive result in a BSE test, her youngest two calves, now part of a different Somerset herd, were culled and tested for BSE, as per TSE1 legislation. Both tested negative for the disease.

Investigations also identified a total of 68 cohort animals that were still alive and that were born or reared with the infected cow during the relevant risk period of 12 months either side of the date of birth of this case.

All these cohort animals have also been culled and all tested negative for BSE.

The affected farm had previous confirmed BSE cases, all of which were born before the reinforced feed ban.

The report concludes that it is likely that these cases were fed feed stored on-farm in silos.

One of the silos has been in continuous use since the early 1980s to store bought cattle feed and was used to store cattle rearing pellets at the time of birth and rearing of this case.

The most likely source is believed to be small amounts of feed, trapped in the silo then dislodging in 2015 or 2016 into the cattle rearer ration that was fed to the infected cow during the first year of her life.

This silo has been decommissioned and the farmer will dispose of it once APHA has sampled it for future testing.

APHA found no evidence to suggest that there has been any further exposure beyond the group of cohort cattle.